No quick fix for raising crop yields

By SUSAN WATTS

CEREAL CROPS which can ‘fix’ their own nitrogen from the environment
have become one of the holy grails of scientists working in agricultural
biotechnology. If genetic engineers could alter the DNA of staple crops
such as wheat and rice in this way, then farmers may no longer need to spread
tonne after tonne of nitrogen fertiliser on their fields.

But by concentrating on nitrogen fixation the biotechnology industry
is not promising to solve any food crises. Reducing the use of fertilisers
would almost certainly cut costs for farmers, and may even help to protect
the environment. But it is only in developing countries, where farmers cannot
afford to use fertilisers today, that yields of crops could be expected
to rise.

The biotechnology community is divided over whether crops which fix
their own nitrogen would produce any more grain than those grown elsewhere
in the developed world with an abundant supply of fertiliser. Many scientists
believe that natural limitations on the photosynthesis which creates energy
in plants will prevent the new technology from raising the yields of such
crops.

Leguminous plants are well adapted to exploit nitrogen from the soil
and air. They to have a symbiotic relationship with bacteria which convert
nitrogen into a form the plants can use. Barry Smith, from the AFRC’s Nitrogen
Fixation Laboratory at the University of Sussex, is trying to shift the
20 genes in these bacteria responsible for nitrogen fixation into the genetic
blueprint of other crops.

This is very difficult. Biotechnologists can usually shift only one
or two genes into new hosts. And, to date, the standard techniques of genetic …

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